One day after he was introduced as the new general manager, he began re-shaping the Giants with swift and decisive force. He fired Marc Ross, the team’s vice president of player evaluation, part of a Saturday blood-letting that also included the cutting of Bobby Hart, the starting right tackle, and the benching of Ereck Flowers, the left tackle.

This is what Gettleman meant Friday when he said “My plan is to come in here every day and kick ass. That’s my plan, OK?’’

OK.

Ross had been with the Giants since 2007 and was closely aligned with Jerry Reese, the former general manager, fired Dec. 4 along with head coach Ben McAdoo. Ross ran the college scouting department and was the point-man for the NFL draft preparation. Ross was not expected to be part of Gettleman’s new management team but in situations such as this, the top college evaluator is often retained until after the draft. The Giants likely will have the No. 2 pick in the 2018 NFL Draft and the immediacy of Ross’ dismissal shows how eager Gettleman is to put his stamp on an organization he previously spent 15 years with, working in the pro personnel department.

“I worked with Marc when I was with the organization before,” Gettleman said. “I have great respect for him and high regard for his work. Clearly, we’re going in a different direction, but that doesn’t make these kinds of decisions any easier.”

Hart was added to the injury report Wednesday with an ankle issue, while Flowers was listed as questionable with a strained groin. Their attitudes all week were not good, according to a source, suggesting both had already mentally checked-out on the season. Neither player practiced Friday even though it was anticipated they would at least try. Gettleman, as the new man in charge, was not having any of that.

For those worried hiring Gettleman would not spark the “wholesale changes’’ co-owner John Mara insisted were necessary with a 2-13 team, this sends a clear message: This is not business as usual. One day after stating “We got to fix the O-line, let’s be honest, let’s not kid each other,’’ Gettleman triggered a major shuffle.

Bobby HartCharles Wenzelberg

Flowers will be replaced as the starting left tackle by rookie Chad Wheeler for the season-finale Sunday against the Redskins, according to a source. Flowers had started every game this season. Another rookie, Adam Bisnowaty, was signed off the practice squad and will start at right tackle in place of Hart, who was officially waived/injured. Bisnowaty, a sixth-round draft pick, will make his NFL debut.

Getting rid of Hart sends a sky-filling flare up inside the Giants locker room, as it shows poor performance and poor attitude will not be tolerated. Hart, a 2015 seventh-round pick from Florida State, started 13 games in 2016 and seven at right tackle this season, including the last three games. Hart, smart but not very strong or athletic, had an inflated opinion of his ability – he called himself “the best right tackle in the league’’ during this year’s training camp.

Flowers has one year remaining on his contract and might not survive Gettleman’s ax – after all, Gettleman did not make him the No.9 pick in the 2015 draft

“Jerry [Reese] was selling you guys Bobby Hart and Flowers working out all winter long,’’ a Giants source told The Post. “Bobby Hart, how bad is he? Not only is he bad on the field, he’s bad in the locker room.’’

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The source said defensive tackle Damon “Snacks’’ Harrison was so angered by Hart’s antics back in the summer that the two almost came to blows.

“They should have let Snacks fight him, then we wouldn’t have had to play with him all year long,’’ the source said. “He was being a punk and he was called out by Snacks and Snacks had to be held back by four big human beings not to beat the living life out of him.’’

Ross last week was one of four candidates interviewed for the general manager position. Under his watch, the Giants drafted cornerstone pieces such as Odell Beckham Jr., Landon Collins, Sterling Shepard, Jason Pierre-Paul and Hakeem Nicks – with Reese always having the final say. There were also draft flops such as Flowers, Owa Odighizuwa, Damontre Moore, Rueben Randle, Jayron Hosley and Marvin Austin, with Eli Apple seemingly on his way to being at the top of the flop list.